Waterflooding method using modified starch granules

ABSTRACT

Adding modified starch granules of a preselected size to the flood water for waterflooding a hydrocarbon containing formation and improving the flood front of said flood water.

EW/912 0R United States Patent [191 Parker et al.

[54] WATERFLOODING METHOD USING MODIFIED STARCI-I GRANULES [75]Inventors: Harry W. Parker, Lubbock, Tex.;

John .W. Marx, Bartlesville, Okla.

[73] Assignee: Phillips Petroleum Company, Bartlesville, Okla.

[22] Filed: Feb. 17, 1971 [21] Appl. No.: 116,216

[52] US. Cl ..l66/275 [51] Int. Cl. ..E2lb 43/25 [58] Field of Search..l66/275, 268, 246, 273, 274

[ 1 Apr. 3, 1973 Primary Examiner-Robert L. Wolfe Attorney-Young & Quigg57 ABSTRACT Adding modified starch granules of a preselected size to theflood water for waterflooding a hydrocarbon containing formation andimproving the flood front of said flood water.

7 Claims, No Drawings WATERFLOODING METHOD USING MODIFIED STARCIIGRANULES This invention relates to a method of waterflooding asubterranean hydrocarbon containing formation. In another aspect, thisinvention improving to the use of modified starch granules for alteringthe injectivity profile of a flood water.

One different problem encountered in waterflooding a hydrocarboncontaining formation is the establishment and maintenance of a uniforminjectivity profile and flood front. A search is continually being madefor plugging agents that have suitable mechanical strength, an abilityto swell upon contact with water, are easy to handle, and are economicalto use.

It is therefore an object of this invention to provide a method ofwaterflooding a hydrocarbon containing formation wherein a pluggingagent is added to the flood water to produce a more uniform injectivityprofile and flood front. Another object of this invention of theabove-described type is to provide improved partial plugs within theformation by utilizing a starch particle plugging agent that hasincreased mechanical strength with no decrease in swelling propertiesrelative to said starch particles before being treated to increase themechanical strength. Other aspects, objects, and advantages of thepresent invention will become apparent from a study of the disclosureand the appended claims.

In the operation of this invention, a subterranean hydrocarboncontaining formation is penetrated by at lease one injection well and atleast one producing well. It should be understood, however, that thisinvention can be practiced where a plurality of producing and injectionwells are utilized to flood and produce a common hydrocarbon containingformation. The relative placements of producing wells are remote fromany injection well and can be in various patterns such as five spot,seven spot, nine spot, etc., as known in the art. A stream of floodwater is injected downwardly through the injection well or wells andinto the formation. A volume of starch granules are contained within atleast a portion of the stream. The injected starch granules have a sizein the range of about 5-32 microns and have been treated to have anincreased mechanical strength with no decrease in swelling propertiesrelative to said starch particles prior to treatment. The fluidsentering the producing well or wells are produced to the surface andcaptured. The starch granules can be continuously injected into theflood water stream or added to the flood water stream at spaced apartlocations to periodically slug the formation with plugging material. Theflood water is preferably brine to reduce the rate of swelling of theparticles during their transportation to the formation. Starch granuleshaving the desired properties and granular size for controlling floodingof the pores of the formation are, for example:

Average granule size Material (diameter) Rice starch 5 micronsCornstarch microns Wheat starch microns Potato starch 32 microns Theparticular type starch granules or mixture thereof can be selected withreference to the size of the pore spaces desired to be plugged. It hasbeen found that granules smaller or larger than the range of 5-32microns are either toolarge or too small and are undesirable forselectively plugging portions of a flooded formation to control theflood front. It has also been found that German rice starch granules arepreferred.

In order to prevent degradation of the starch material, bactericides canbe added to the flood water stream. Bactericides that can be used withthis invention are, for example:

Formaldehyde Chloroform Other commercially available bactericides.

For brine flood waters containing in excess of about 80,000 parts permillion NaCl or substantial equivalent such as, for example, MgCl CaclKC], etc., there is substantially no biodegradation either in theatmosphere or under anaerobic reservoir conditions. In this flood water,a bactericide need not be added to the flood water starch mixture. Forbrines containing about 50,00080,000 ppm salts, as set forth above,there is some biodegradation of the starch. This degradation isnegligible in the atmosphere, but in some reservoirs, a bactericide maybe preferred. However, for fresh water and brines having less than about5000 ppm salts, as set forth above, it is preferred to mix 0.175 to 1.75pounds of formaldehyde or chloroform per 42-gallon barrel of floodwater.

The treatment method of modifying the starch granules to produceresultant granules having increased strength while not decreasing theirswelling properties can be cross-linking said particles by treatmentwith epichlorohydrin, formaldehyde, organic dihalides, and otherproducts as described, for example, in US. Pat. No. 2,500,950 and theEncyclopedia of Chemical Technology, Vol. 12, l954,p. 776.

The following examples are some preferred treating methods of thisinvention for improving the configuration of the flood front.

EXAMPLE I Injecting about 0.05-0.5 pore volume of a 250-5 ,000 ppmstarch granule suspension per barrel of flood water over a lto 6-monthperiod into a formation through a water injection well of a waterfloodoperation.

EXAMPLE II Injecting a slug of about 200-500 barrels of flood waterhaving suspended therein 500l0,000 ppm starch granules through a waterinjection well of a waterflood operation and into the formation adjacentthereto.

EXAMPLE Ill Injecting a slug of about 200-5000 barrels of flood waterhaving suspended therein SOD-10,000 ppm starch granules through aproducing well and into the formation adjacent thereto for restrictingand reducing the influx of water from natural sources or from awaterflood. This slug of material can also be moved through theformation to desired positions spaced from the well bore as recommendedby reservoir studies and the mechanical conditions of the downholeequipment and the formation.

German rice starch having a particle size of 25-30 microns can betreated with formaldehyde and cross linked to increase the mechanicalstrength thereof by at least percent. The granules can then be dispersedin sodium chloride brine and injected without filtration into theformation.

By injecting starch particles that have been treated for increasing thestrength of said particles, selective plugging of the formation can beaccomplished which is more durable and longer lastingagainst fluiddynamics within the formation, thereby making possible the forming andmaintenance of a more uniform and desirable flood front. Without acontrolled flood front, volumes of oil will be by-passed and leftunrecovered in the formation.

Other modifications and alterations of this invention will becomeapparent to those skilled in the art from the foregoing discussion andit should be understOod that this invention is not to be unduly limitedthereto.

What is claimed is:

l. A method for recovering hydrocarbons from subterranean hydrocarboncontaining formations penetrated by at least one injection well and atleast one remotely located producing well, comprising:

injecting downwardly through the injection well and into the formation astream of flood water having contained in at least a portion of saidstream a volume of starch granules having a size in the range of about5-32 microns with said granules being cross-linked to have an increasedmechanical strength and substantially no decrease in swellingproperties; and

producing to the surface the fluid entering the producing well.

2. A method, as set forth in claim 1, wherein the starch granules areselected from at least one of a group of rice starch, cornstarch, wheatstarch and potato starch.

3. A method, as set forth in claim 1, wherein the starch granules areintermittently added to the flood water stream at spaced apartlocations.

4. A method, as set forth in claim 1, wherein the flood water is brine.

S. A method, as set forth in claim 1, wherein the bactericides are addedto the flood water stream to prevent degradation of the starch materialwithin the formation.

6. A method, as set forth in claim 1, wherein the flood water stream isinjected into a plurality of injection wells and fluids are producedthrough a plurality of producing wells.

7. A method for recovering hydrocarbons from subterraneanhydrocarbon-containing formatIons penetrated by at least one injectionwell and at least one remotely located producing well, comprising:

injecting downwardly through the injection well and into the formation astream of flood water haVing suspended in at least a portion of saidstream a volume of starch granules having a size in the rangeof about5-32 microns with said granules being crosslinked to have anincreased'mechanical strength and substantially no decrease in swellingproperties, said granules being cross-linked with at least one ofepichlorohydrin, formaldehyde, an organic dihalide, or an alkyl ester;and

producing to the surface fluid entering the producing well.

2. A method, as set forth in claim 1, wherein the starch granules are selected from at least one of a group of rice starch, cornstarch, wheat starch and potato starch.
 3. A method, as set forth in claim 1, wherein the starch granules are intermittently added to the flood water stream at spaced apart locations.
 4. A method, as set forth in claim 1, wherein the flood water is brine.
 5. A method, as set forth in claim 1, wherein the bactericides are added to the flood water stream to prevent degradation of the starch material within the formation.
 6. A method, as set forth in claim 1, wherein the flood water stream is injected into a plurality of injection wells and fluids are produced through a plurality of producing wells.
 7. A method for recovering hydrocarbons from subterranean hydrocarbon-containing formatIons penetrated by at least one injection well and at least one remotely located producing well, comprising: injecting downwardly through the injection well and into the formation a stream of flood water haVing suspended in at least a portion of said stream a volume of starch granules having a size in the range of about 5-32 microns with said granules being crosslinked to have an increased mechanical strength and substantially no decrease in swelling properties, said granules being cross-linked with at least one of epichlorohydrin, formaldehyde, an organic dihalide, or an alkyl ester; and producing to the surface fluid entering the producing well. 